HTTP/2: send WINDOW_UPDATE instead of RST_STREAM with NO_ERROR.

HTTP/2: send WINDOW_UPDATE instead of RST_STREAM with NO_ERROR.

After the 92464ebace8e change, it has been discovered that not all
clients follow the RFC and handle RST_STREAM with NO_ERROR properly.

Notably, Chrome currently interprets it as INTERNAL_ERROR and discards
the response.

As a workaround, instead of RST_STREAM the maximum stream window update
will be sent, which will let client to send up to 2 GB of a request body
data before getting stuck on flow control.  All the received data will
be silently discarded.

See for details:
http://mailman.nginx.org/pipermail/nginx-devel/2016-April/008143.html
https://bugs.chromium.org/p/chromium/issues/detail?id=603182